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Abstract

This thesis presents an analysis of a pollution episode in an urban atmosphere, using a complex model system. The model system simulates the atmospheric conditions during a measurement campaign, called FLUMOB, in July 1994 in the area of Berlin-Brandenburg during a distinct summer smog situation.
The model system consists of a non-hydrostatic atmosphere-chemistry model that is nested into a coarser regional atmosphere-chemistry model which, in turn, is embedded in an even coarser framework. Thus, a chain of mesoscale atmosphere-chemistry models is applied to the regions of Europe, Germany and Berlin-Brandenburg, respectively. The simulation at the highest resolution is used to analyse the polluted urban atmosphere in Berlin-Brandenburg while the observational data sets are used for model evaluation.
The analysis of the field measurements made during the FLUMOB campaign shows that naturally emitted hydrocarbons play the dominant role in the ozone formation in Berlin-Brandenburg. The composition of non-methane volatile organic compounds in the investigated area is dominated (70-80Vo) by biogenically emitted hydrocarbons. During the analysed case, ozone formation was sensitive to hydrocarbon concentrations so that the ozone production was limited by the availability of hydrocarbons and thus especially by the amount which were biogenically emitted. Furthermore it is shown that the FLUMOB episode was influenced by elevated concentrations ofozone in the free troposphere. In contrast to previous analysis the importance of ozone produced outside Europe is stressed. In spite of the stagnant high pressure situation which occurred during the FLUMOB episode, Germany was significantly influenced by long-range transport of ozone. This transport also influenced the near surface ozone concentrations.
The model evaluation suggests the high quality of simulated urban ozone and nitrogen species and hence of the anthropogenic emission inventory. The total amount of ozone is, however, underpredicted by the model for two reasons: Underprediction of biogenic hydrocarbon emissions and uncertainties of the chemical information at the lateral boundaries of the European domain.